Abstract: Aim To deduce the approximate functions of fatigue fracture probability, reliability and fatigue lifetime, and make nonequibrium statistical theory of fatigue fracture applicable to real metals. Methods Using the concept and method of nonequibrium statistical theory with microdynamics, the more rigorous mathematical calculation was made. Results The approximate functions of fatigue fracture probability, reliability and fatigue lifetime were obtained. Conclusion The fatigue lifetime of all real metals can be expressed by the same formula, although the f(N) has the different expression.